(1) Field of the Invention
This invention relates to a method of encoding facsimile signal where the quality of reproduced picture images can be freely selected from the receiver side. The invention relates more particularly to a novel encoding method which is suitable when a facsimile terminal is connected with a display unit for conversational mode communication or for picture image data base retrieval.
(2) Description of the Prior Art
Facsimile communication in prior art is the communication from paper to paper with the image of print-out copies. As facsimile communication has been diversified in recent years, a facsimile terminal will be increasingly combined with a display unit for conversational mode picture image communication or picture image data base retrieval. Conventional method which reproduces information consecutively according to the order of scanning lines on a display unit and completes the whole picture image as the scanning of all lines ends may be used for this type of facsimile communication. Alternatively, it is possible to adopt a sequential method which first displays a rough whole image at a higher speed and improves the picture quality gradually thereafter.
In the latter method, receivers can judge if the displayed data satisfies them or not at the early stage when the rough picture image is displayed, and if that is not the desired data, they can stop data transmission so as to save trouble. If the displayed data is the desired one, on the other hand, receivers can continue receiving the transmission until the quality improves to a satisfactory level. They can print out, if necessary, the picture image by using a facsimile terminal. The sequential reproduction method is, therefore, extremely advantageous as it allows free selection of picture quality, faster retrieval and effective use of transmission channels.